Populations of western toad (Bufo boreas) have declined or disappeared from much of the species' range in the United States. To assess distributions and densities of the western toad in the foothills of west-central Alberta, Canada, we conducted visual surveys of 130 natural water bodies in watersheds encompassing a range of human-disturbance levels in early and late summer 2000. Encounter rates were consistently low throughout the study area (0.2 to 0.3 toads/h) and were one-tenth the rate for the co-occurring wood frog (Rana sylvatica). Pitfall trapping of breeding and non-breeding sites during 2001 and 2002 showed differences in age structures between western toad and wood frog populations and low recruitment of newly metamorphosed juveniles into western toad populations. On ponds, more toads of ≥1 y old were captured than recently emerged juveniles. The difference between the 2 age classes was greater on ‘borrow pits’ (human-created roadside ponds) than on beaver ponds, suggesting that borrow pits might be population sinks providing poor larval habitat. Borrow pits either dried prior to juvenile emergence or had oligotrophic to mesotrophic waters compared to eutrophic conditions in beaver ponds. Pond creation as a mitigation strategy or by-product of road construction may put western toad populations at risk of decline in the foothills of Alberta.
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